Much of the water on planet Earth and throughout our solar system is old, so old it probably predates the birth of our sun, a study suggests.

As much as 30 to 50 percent of the water now on Earth may have originated in interstellar space and been in the original cloud of dust that first formed our sun and then the planets, scientists say.

The sun grabbed most of that cloud as it was being born, but enough was left over to form a protoplanetary disk out of which the solar system's planets would form.

The question had been whether the hot, violent process of the sun's birth would have consumed and destroyed all the water in the original cosmic cloud, or whether some remained in the protoplanetary disk as it began creating the planets.

The new study suggests it did, and that water is commonly incorporated into newly forming planets throughout the Milky Way galaxy and beyond, the researchers report in the journal Science.

"This is speculative, but if the sun's formation was typical -- and we have no reason to think it wasn't -- then the fact that this water survived the formation of a star means that they can survive it everywhere," says study first author Ilse Cleeves, a doctoral candidate at the University of Michigan.

If so, it could increase our chances of finding life on distant planets, the researchers say.

"If water in the early solar system was primarily inherited as ice from interstellar space, then it is likely that similar ices, along with the prebiotic organic matter that they contain, are abundant in most or all protoplanetary disks around forming stars," says study co-author Conel Alexander of the Carnegie Institution for Science in Washington, D.C.

Water is found throughout the Solar System, not solely on Earth. It has been detected on icy comets and moons, and even in the shadowed basins of Mercury, the closest planet to the Sun. Water has been found within mineral samples from the Moon, Mars and meteorites.

"Our findings show that a significant fraction of our Solar System's water, the most-fundamental ingredient to fostering life, is older than the Sun, which indicates that abundant, organic-rich interstellar ices should probably be found in all young planetary systems," Alexander says.

That water survived the birth of the solar system supports the idea that interstellar organic matter likely did as well, strengthening the case for such matter to have subsequently reached the earth in comets and meteorites.